Hey Laralike - yes, I am very familiar with this feeling. I played a lot of games ranking up from 20 kyu to 15 kyu that felt a LOT like this - and the similarity between them was that when I reviewed the game, I realized that I was already behind by Move 50, and never recovered (or went even further downhill from there…)
The problem here is that the Opening is such a deceptively slippery part of the game - in that one person can very quickly grab a huge advantage at the very beginning, and those can be difficult to see early on because it feels like so much of the board is up for grabs.
The other thing that makes the strategic landscape difficult to understand and interpret is that a single move can have multiple consequences. For instance - if your opponent grabs two corner enclosures with an empty side between them, they are also implicitly threatening to create a large extension between those corners. You have to train yourself to not only spot the immediate consequences (i.e. my opponent now has two enclosed corners) but look ahead and see other dangerous potential consequences down the road.
As such, it really helps to approach the Opening with something like a checklist in mind.
So, you start with an empty board, and you ask yourself:
Are there unclaimed corners?
If YES - claim a corner
If NO - can I enclose a corner I’ve claimed or approach an opponent’s corner? Which is bigger? Can I create a situation where I can potentially make a large extension along one side from two corners? Can I prevent a situation where my opponent creates an extension along one side? Which is bigger?
Once all corners have been approached or enclosed:
Can I create a large extension or prevent a large extension? Which is bigger?
Is there a place where I can get an advantage going from Opening into Early Midgame by expanding my corner or side extension into a big enclosure? Is there a place where my opponent could create a big enclosure that I could still prevent? Which is bigger?
I’m going to reference a few moments from your attached game as examples.
So, starting off, the first 8 moves played in the game were both sides enclosing corners. Personally, (your mileage may vary) I find that “enclose corners first” is a strategy that works best if you’re expecting a very fight heavy game, and you want some cash in your pocket right off the bat.
In this game, seeing as your opponent already enclosed the upper right corner with Move 5, it might have been more effective to approach their lower right corner like this rather than trying to enclose your own corner
This way you not only approach the corner, but you also prevent the potential of a large extension along the right side. IMHO being able to get two benefits is bigger than the one benefit of enclosing your own corner.
You had a similar situation at Move 12. Black had just read the situation and prevented you from making a large extension on the left side. You chose to protect / enclose your lower left corner.
Another option would have been to play on the right side to prevent a large extension
One quick side note, you did play on the right side with Move 14, but then instead of making a base with Move 16, you tried to make a threatening / sente move that left your two stones dangerously far apart. If you had made a base (i.e. playing a safe 2 space jump between stones) then your opponent would have tenuki’ed and grabbed something else. Because you left cut points between your stones, it was more lucrative for Black to attack you and expand their lower corner away from the edge while you scrambled to make a base.
One last example, and then I’m going to wrap up. This is one of those moments that I was referencing above that are REALLY HARD TO SEE when you’re playing because you’re focused on the local exchange, and you miss something that might potentially be happening somewhere else:
On one hand, it seems like Black is chasing your right side group, and it feels like it requires a local response. However, at the same time, Black is already expanding their upper right potential away from the edge and into the middle. If they play anywhere on the upper right side they could create a huge corner enclosure.
Because your right side group isn’t in immediate danger of getting killed (i.e. you can still try to make eyes at the edge or run out into the middle) preventing that potential enclosure becomes the bigger priority. I’ve marked the AI suggested moves with O’s.
You can play it risky and attach at O17 and then run out to the left when attacked, or you can just make a large extension from your upper left corner at K16 (or other moves around there)
If you’d like to read more about that Opening priorities checklist, and how to weigh them against each other, I wrote this installment of the 19x19 FOR BEGINNERS series about it here:
Good luck!